کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5516252 | 1542569 | 2017 | 12 صفحه PDF | دانلود رایگان |
- Long-term nitrogen load decreased forest soil microbial biomass and respiration.
- Soil enzyme activities were affected by long-term nitrogen loading.
- Long-term nitrogen load induced shifts in soil phospholipid fatty acids.
- Soil microbial variables were similar despite varying ecosystem nitrogen retention.
Microbial communities in the organic horizon (O-horizon) of forest soils play key roles in terrestrial nitrogen (N) cycling, but effects on them of long-term high N loading, by N deposition or experimental addition, are not fully understood. Thus, we investigated N-loading effects on soil microbial biomass N, carbon (C) and phosphorus stoichiometry, hydrolytic and oxidative enzymes, community composition (via phospholipid fatty acids, PLFA) and soil chemistry of the O-horizon in study plots of three well-studied experimental Norway spruce (Picea abies) forests in Sweden and the Czech Republic. These forests span substantial gradients in current N deposition, experimental N addition and nitrate (NO3â) leaching. Current N deposition ranges from â¼3 kg haâ1 yearâ1 of N in central Sweden (StrÃ¥san) to â¼15 kg haâ1 yearâ1 of N in SW Sweden (Skogaby) and Czech Republic (Äertovo). Furthermore, accumulated historical N loading during 1950-2000 (which include experimental N addition performed at StrÃ¥san and Skogaby) ranged â¼200-â¼2000 kg haâ1 of N. Across all sites and treatments, current NO3â leaching ranged from low (â¼0.1 kg haâ1 yearâ1 of N) at StrÃ¥san, to high (â¼15 kg haâ1 yearâ1 of N) at Skogaby and Äertovo. We found significantly lower C/N ratios and greater amounts of extractable inorganic N species in the forest soils' O-horizons at the high N loading plots. Microbial biomass and basal respiration decreased under experimental N addition treatments and tended to decrease with increased N deposition. Similarly, activities of hydrolytic enzyme activity associated with N acquisition were lower, although differences in activities at specific sites with the highest and intermediate historical N deposition levels failed statistical significance. Conversely, activities of soil hydrolytic enzymes associated with C acquisition were greater in study plots exposed high N loading. PLFA profiles indicated shifts in microbial community composition induced by long-term N load, towards higher and lower relative abundance of Gram-positive and Gram-negative bacteria, respectively (but no changes in fungal relative abundance). Taken together, our results suggest that long-term N loading of N-limited Norway spruce forests aggravates limitation of other resources, likely of C, for soil microbial communities. Although microbial variables in the soil O-horizon differed between plots exposed to low and high current N loading, microbial variables in plots that leached small amounts and large amounts of NO3â exposed to high N load were similar.
Journal: Soil Biology and Biochemistry - Volume 115, December 2017, Pages 310-321